//
//  6532.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 19/06/2016.
//  Copyright 2016 Thomas Harte. All rights reserved.
//

#pragma once

#include "ClockReceiver/ClockReceiver.hpp"

#include <cstdint>
#include <cstdio>

namespace MOS {

/*!
	Implements a template for emulation of the MOS 6532 RAM-I/O-Timer ('RIOT').

	The RIOT provides:
		* 128 bytes of static RAM;
		* an interval timer; and
		* two digital input/output ports.

	Consumers should derive their own curiously-recurring-template-pattern subclass,
	implementing bus communications as required.
*/
template <class T> class MOS6532 {
public:
	inline void set_ram(uint16_t address, uint8_t value)	{	ram_[address&0x7f] = value;		}
	inline uint8_t get_ram(uint16_t address)				{	return ram_[address & 0x7f];	}

	inline void write(int address, uint8_t value) {
		const uint8_t decodedAddress = address & 0x07;
		switch(decodedAddress) {
			// Port output
			case 0x00: case 0x02:
				port_[decodedAddress / 2].output = value;
				static_cast<T *>(this)->set_port_output(
					decodedAddress / 2,
					port_[decodedAddress/2].output, port_[decodedAddress / 2].output_mask
				);
				set_port_did_change(decodedAddress / 2);
			break;
			case 0x01: case 0x03:
				port_[decodedAddress / 2].output_mask = value;
				static_cast<T *>(this)->set_port_output(
					decodedAddress / 2, port_[decodedAddress/2].output,
					port_[decodedAddress / 2].output_mask
				);
				set_port_did_change(decodedAddress / 2);
			break;

			// The timer and edge detect control
			case 0x04: case 0x05: case 0x06: case 0x07:
				if(address & 0x10) {
					timer_.writtenShift = timer_.activeShift =
						(decodedAddress - 0x04) * 3 + (decodedAddress / 0x07);	// i.e. 0, 3, 6, 10
					timer_.value = (unsigned(value) << timer_.activeShift) ;
					timer_.interrupt_enabled = !!(address&0x08);
					interrupt_status_ &= ~InterruptFlag::Timer;
					evaluate_interrupts();
				} else {
					a7_interrupt_.enabled = !!(address&0x2);
					a7_interrupt_.active_on_positive = !!(address & 0x01);
				}
			break;
		}
	}

	inline uint8_t read(int address) {
		const uint8_t decodedAddress = address & 0x7;
		switch(decodedAddress) {
			// Port input
			case 0x00: case 0x02: {
				const int port = decodedAddress / 2;
				uint8_t input = static_cast<T *>(this)->get_port_input(port);
				return (input & ~port_[port].output_mask) | (port_[port].output & port_[port].output_mask);
			}
			break;
			case 0x01: case 0x03:
				return port_[decodedAddress / 2].output_mask;
			break;

			// Timer and interrupt control
			case 0x04: case 0x06: {
				uint8_t value = uint8_t(timer_.value >> timer_.activeShift);
				timer_.interrupt_enabled = !!(address&0x08);
				interrupt_status_ &= ~InterruptFlag::Timer;
				evaluate_interrupts();

				if(timer_.activeShift != timer_.writtenShift) {
					unsigned int shift = timer_.writtenShift - timer_.activeShift;
					timer_.value = (timer_.value << shift) | ((1 << shift) - 1);
					timer_.activeShift = timer_.writtenShift;
				}

				return value;
			}
			break;

			case 0x05: case 0x07: {
				uint8_t value = interrupt_status_;
				interrupt_status_ &= ~InterruptFlag::PA7;
				evaluate_interrupts();
				return value;
			}
			break;
		}

		return 0xff;
	}

	inline void run_for(const Cycles cycles) {
		unsigned int number_of_cycles = unsigned(cycles.as_integral());

		// permit counting _to_ zero; counting _through_ zero initiates the other behaviour
		if(timer_.value >= number_of_cycles) {
			timer_.value -= number_of_cycles;
		} else {
			number_of_cycles -= timer_.value;
			timer_.value = (0x100 - number_of_cycles) & 0xff;
			timer_.activeShift = 0;
			interrupt_status_ |= InterruptFlag::Timer;
			evaluate_interrupts();
		}
	}

	MOS6532() {
		timer_.value = unsigned((rand() & 0xff) << 10);
	}

	inline void set_port_did_change(int port) {
		if(!port) {
			uint8_t new_port_a_value =
				(get_port_input(0) & ~port_[0].output_mask) |
				(port_[0].output & port_[0].output_mask);
			uint8_t difference = new_port_a_value ^ a7_interrupt_.last_port_value;
			a7_interrupt_.last_port_value = new_port_a_value;
			if(difference&0x80) {
				if(
					((new_port_a_value&0x80) && a7_interrupt_.active_on_positive) ||
					(!(new_port_a_value&0x80) && !a7_interrupt_.active_on_positive)
				) {
					interrupt_status_ |= InterruptFlag::PA7;
					evaluate_interrupts();
				}
			}
		}
	}

	inline bool get_inerrupt_line() const {
		return interrupt_line_;
	}

private:
	uint8_t ram_[128];

	struct {
		unsigned int value;
		unsigned int activeShift = 10, writtenShift = 10;
		bool interrupt_enabled = false;
	} timer_;

	struct {
		bool enabled = false;
		bool active_on_positive = false;
		uint8_t last_port_value = 0;
	} a7_interrupt_;

	struct {
		uint8_t output_mask = 0, output = 0;
	} port_[2];

	uint8_t interrupt_status_ = 0;
	enum InterruptFlag: uint8_t {
		Timer = 0x80,
		PA7 = 0x40
	};
	bool interrupt_line_ = false;

	// Expected to be overridden.
	void set_port_output(
		[[maybe_unused]] int port,
		[[maybe_unused]] uint8_t value,
		[[maybe_unused]] uint8_t output_mask
	) {}
	uint8_t get_port_input([[maybe_unused]] int port) {
		return 0xff;
	}
	void set_irq_line(bool) {}

	inline void evaluate_interrupts() {
		interrupt_line_ =
			((interrupt_status_&InterruptFlag::Timer) && timer_.interrupt_enabled) ||
			((interrupt_status_&InterruptFlag::PA7) && a7_interrupt_.enabled);
		set_irq_line(interrupt_line_);
	}
};

}
